1. Field of Invention
The present invention relates to a wire printing device wherein wires are individually movable lengthwise towards a platen by means of electromagnets, to print on a recording medium backed by said platen, typically through an inked ribbon, characters are built up by the selective printing of elementary dots. It is necessary to provide lateral support for the wires; this may be done by a terminal guide which guides the ends of the wires near the platen and an intermediate guide which guides the wires between the electromagnets and the terminal guide. The problem of lubricating the wires in the guides then arises. Another problem arising in this printing devices is that the terminal guide is very subject to wear, whereby lowering the operating life of the device.
2. Description of the Prior Art
A device is known in which the intermediate guide supports the wires along the entire length between the terminal guide and the armatures of the electromagnets. In this device, a chamber normally filled with lubricating grease and through which all the wires pass is formed in the rear part of the intermediate guide for the wires, rear meaning nearer the platen. As a result of the presence of the lubricant, the friction between the wires and the guides is reduced. Moreover, the ink contained in the inked ribbon disposed between the terminal guide and the recording medium is largely prevented from running back along the printing wires by capillarity, with a consequent reduction of smooth running and the risk of binding of the wires once the ink dries. This printing device, however, has the drawback that, after a fairly brief period of operation, part of the ink in the inked ribbon migrates to the chamber, fouling the grease contained therein; the fouled grease no longer lubricates effectively and is less effective in preventing the ink from running back along the printing wires. Moreover, the replacement of the fouled grease is difficult and laborious.
Another device is known in which the terminal guide for the wires is constituted by two small opposed plates, one of which is fixed to the supporting frame and has a sawtooth-shaped profile for guiding the wires, while the other plate has a substantially plane opposed surface and is pivoted on the supporting frame to hold the wires seated in the notches in the fixed plate, being biased by a compression spring. In this device, only one of the two guide plates is exchangeable, not without difficulty, thus only partially solving the aforesaid problem.